1. Field of the Invention
The present invention relates to a passive seat belt arrangement for a vehicle. The present invention particularly relates to the passive seat belt arrangement for the vehicle wherein a seat belt extending around the vehicle occupant's body is automatically transferred to a release state only when the vehicle occupant starts to try to get off the vehicle seat.
2. Description of the Prior Art
A conventional passive seat belt arrangement for vehicles in which, upon opening open or closure of a vehicle door, a passive-type seat belt for releasably restraining a a vehicle occupant in their seat is automatically released from the occupant or automatically fitted around the occupant's body is exemplified by a Japanese Patent Application Second Publication (Tokkou) Sho No. 60-6817 published on Feb. 20, 1985. In the above-identified Japanese Patent Application Publication, a door locked state detection sensor is provided at a door lock mechanism for detecting whether a door lock operation member of the lock mechanism of the vehicle door is operated and the passive seat belt is, at this time, actuated to release from the occupant's body portion according to a detection result of the door locked state detection sensor and a switched state of a door switch for detecting an open state of the vehicle door.
Therefore, if the vehicle door spontaneously opens and the door switch is turned on due to a deformation of the door, e.g., at the time of collision of the vehicle against an obstacle, the passive seat belt will not be actuated to release from the occupant's body portion due to the installation of the door locked state detection sensor in addition to the door switch. The seat belt is fitted or released to or from the occupant's body portion in response to an actuation operation by means of a seat belt motor only when the door locked state detection sensor detects the release of the door locked state and the door switch detects the open state of the vehicle door is turned on.
In such a conventional passive seat belt arrangement as described above, the above-described automatic release operation of the seat belt from the occupant's body portion will not occur even if the door switch spontaneously turns on due to the deformation of the door at the time of collision against the obstacle so that safety of the vehicle occupant is secured, e.g., against a traffic accident. However, if the occupant or another person fails to lock the door, the effect of automatic release operation of the passive seat belt arrangement cannot be exhibited since the lock mechanism is not operated. Although some automotive vehicles adopt an automatic door lock mechanism interlocked with the vehicle speed, it will lead to increased of a manufacturing cost for such passive seat belt arrangements and will be unsafe below the actuating vehicle speed.